Process for the preparation of phenol by means of the hydrodeoxygenation of benzene-diols

Abstract

A process is described for the preparation of phenol characterized in that the phenol is obtained by means of the hydrodeoxygenation of benzene-diols with hydrogen, operating in continuous, in an aqueous solution, at temperatures ranging from 250 to 500° C., at pressures of 1-100 bar and in the presence of a catalyst based on elements of group VIB or group VIII of the periodic table.

1. A process for the preparation of phenol, characterized in that the phenol is obtained by the hydrodeoxygenation of a benzene-diol with hydrogen, operating continuously, in aqueous solution, at temperatures ranging from 250 to 500° C., at pressures of 1-100 bar and in the presence of a catalyst comprising an element of group VIB or their mixtures, or group VIII of the periodic table or their mixtures. 
     
     
       2. The process according to  claim 1 , wherein the benzene-diol is selected from 1,2-benzene-diol, 1,3benzene-diol, 1,4-benzene-diol and their mixtures. 
     
     
       3. The process according to  claim 1 , wherein the reaction is carried out in vapour phase at a temperature of 300-450° C., at a pressure of 3-50 bar and a space velocity expressed as kg of benzene-diols/h/kg of catalyst of 0.1-10 h −1 . 
     
     
       4. The process according to  claim 3 , wherein the reaction is carried out at a space velocity of 0.5-5 h −1 . 
     
     
       5. The process according to  claim 1 , wherein the reaction is carried out inside an adiabatic fixed bed reactor containing the catalyst, in which a stream comprising an aqueous solution of benzene-diol is fed, at concentrations ranging from 5 to 60% by weight, together with a stream of hydrogen, in such a quantity that the ratio between the total moles of hydrogen and benzene-diols ranges from 2:1 to 50:1. 
     
     
       6. The process according to  claim 5 , wherein an aqueous solution of benzene-diols is fed into the reactor, at concentrations ranging from 10 to 40% and a stream of hydrogen in such a quantity that the ratio between the total moles of hydrogen and benzene-diols ranges from 5:1 to 30:1. 
     
     
       7. The process according to  claim 5 , wherein the feeding stream is vapourized and heated to a temperature ranging from 250 to 500° C. and the pressure is kept at a value ranging from 1 to 100 bar. 
     
     
       8. The process according to  claim 1 , wherein the catalyst comprises at least one element selected from molybdenum and tungsten. 
     
     
       9. The process according to  claim 1 , wherein the catalyst comprises an element of group VIB and further comprises, as promoters, an element selected from those belonging to group VIII, phosphorous of their mixtures. 
     
     
       10. The process according to  claim 9 , wherein the catalyst comprises a promoter of group VIII selected from nickel, cobalt, iron and ruthenium. 
     
     
       11. The process according to  claim 1 , wherein the catalyst comprises at least one element selected from cobalt, palladium, nickel, and platinum. 
     
     
       12. The process according to  claim 1 , wherein the catalyst comprises at least one element of group VIII and further comprises, as promoters, an element selected from zinc, rhenium, selenium, tin, germanium, lead and their mixtures. 
     
     
       13. The process according to  claim 1 ,  9  or  12 , wherein the catalyst is deposited on a carrier. 
     
     
       14. The process according to  claim 13 , wherein the carrier is selected from alumina, silica, titanium dioxide, crystalline or amorphous alumino-silicates, crystalline spinels or their mixtures. 
     
     
       15. The process according to  claim 13 , wherein the catalyst based on an element of group VIB is present on the carrier at a concentration ranging from 1 to 50% by weight and the promoters of these catalysts at concentrations ranging from 0.1 to 100% atomic with respect to the element of group VIB. 
     
     
       16. The process according to  claim 15 , wherein the catalyst based on an element of group VIB is present on the carrier at a concentration ranging from 3 to 30% by weight and the promoters of these catalysts at concentrations ranging from 1 to 50% atomic with respect to the element of group VIB. 
     
     
       17. The process according to  claim 13 , wherein the catalyst based on an element of group VIII is present on the carrier at a concentration ranging from 0.05 to 20% by weight and the promoters of these catalysts at concentrations ranging from 0.5 to 200% atomic with respect to the element of group VIII. 
     
     
       18. The process according to  claim 17 , wherein the catalyst based on an element of group VIII is present on the carrier at a concentration ranging from 0.1 to 10% by weight and the promoters of these catalysts at concentrations ranging from 1 to 120% atomic with respect to the element of group VIII. 
     
     
       19. The process according to  claim 1 , wherein the reaction is carried out in two or more adiabatic fixed bed reactors in series, by cooling the stream leaving one reactor before entering the subsequent one, in order to limit the temperature increase in each reactor to a value of less than 40° C. 
     
     
       20. The process according to  claim 19 , wherein both the feeding of water and that of hydrogen are partialized to the single reactors, operating so that the temperature increase in each reactor does not exceed 40° C. 
     
     
       21. The process according to  claim 19 , wherein the reaction is carried out in two reactors which are alternately inserted in reaction and regeneration. 
     
     
       22. The process according to  claim 1 , wherein the catalysts are subjected to regeneration by means of combustion at a temperature ranging from 400 to 550° C. and a pressure ranging from 1 to 3 bar, with mixtures of oxygen and nitrogen in a ratio ranging from 0.1 to 20% by volume and a space velocity, expressed in 1 of gas mixture/h/l of catalyst, equal to 3000÷6000 h −1 . 
     
     
       23. The process according to  claim 22 , wherein the regeneration is carried out in the same reactor in which the catalyst is placed for the reaction.